refactor(presence): execute the extinction_sec/anneal_sec withdrawal

docs/SPEC.md specified this removal, listed its parts, and ended "grep
for both names and expect no survivors". There were about forty.
docs/requirements.md meanwhile recorded both constants as Withdrawn and
"deleted rather than retained at zero", on the grounds that a field
naming a mechanism the pipeline no longer has is actively misleading.
Neither statement was true of the code: Config still carried
extinction_sec 57.4 and anneal_sec 35.5, --extinction and --anneal still
parsed, and SceneTrackerFunc still ran its keep-alive in both shipped
pipelines, announcing its timeout at every startup.

SceneTrackerFunc is replaced by FrameAnnotationFunc, which is stateless:
same ports, same output type, no keep-alive. Presence belongs to
TrackRegistry (AR-012), where a window is the extent of a track an actor
owned and ends at the last sighting (AR-013). The keep-alive answered
that question a second time and answered it worse, by re-opening exactly
the trailing cool-down AR-013 refuses.

Visible change: --verbosity standard's frames[].identified listed every
actor inside the keep-alive, including ones absent from the frame. It
now lists what was matched in that frame. Minimal and xray output is
untouched -- both were already built from registry claims and never
consulted this node. No schema bump: the published extraction block
reports track_extinction_sec, a different knob that bounds
re-association and never extends a claim.

TrackRegistry::Config::extinction_sec is renamed track_extinction_sec to
match the Config field feeding it, so the grep SPEC.md asks for now
returns nothing rather than one confusing false positive.

Two targets turned out to have been silently dead, both since the
AR-007/AR-008 tracker redesign, and both for the same reason -- they
construct FaceTrackerFunc from a Config alone, a signature that stopped
existing when association moved into probability space:

- scene_preview is fixed here. It now mirrors main.cpp's construction
  order exactly (matcher, then registry, then tracker) and wires the
  registry's claims into the sink, which it was not doing. DP-001 says
  modes are front-ends that must not fork pipeline logic; this one had
  forked it and then rotted.
- sae_kpn is not fixed. Restructuring the seam so the tracker can reach
  a calibration that only exists once the matcher is built is VR-011's
  rewrite, not a patch, and presence claims do not cross the seam at all
  today. It is now behind SAE_BUILD_KPN_BINDINGS=OFF with the reason
  recorded, so `cmake --build` succeeds and the breakage is attributed
  rather than rediscovered.

That second one is worth stating plainly: VR-002 ("replay drives the
real KPN nodes, not a reimplementation") is marked Done, and the module
that makes replay possible has not compiled for some time. The .so in a
stale build/ predates the change.

Python side: the two names are gone from optimize.py, replay.py and
run_holdout_all_models.py as Config keys. anneal_sec survives as
REPLAY_LOCAL_KEYS -- it still configures replay.py's own windowing,
which is a Python reimplementation that no longer matches the sink and
is documented as such. That divergence is VR-011's.

TRACES: AR-012, AR-013 | DP-001 | SR-002

src/nodes/frame_annotation_node.hpp

@@ -0,0 +1,43 @@
+#pragma once
+/// TRACES: AR-012, AR-013 | SR-002
+///
+/// FrameAnnotationFunc — project a matched frame into a per-frame annotation.
+///
+/// Stateless, and that is the entire point of it.
+///
+/// It replaces `SceneTrackerFunc`, which kept an extinction timer per actor and
+/// reported an actor as visible for `extinction_sec` (57.4 s) after their last
+/// detection. docs/SPEC.md specified that node's deletion -- "anneal_sec and
+/// extinction_sec are deleted, not re-tuned ... SceneTrackerFunc goes with
+/// them", with a removal list ending "grep for both names and expect no
+/// survivors" -- and docs/requirements.md recorded both constants as Withdrawn,
+/// deleted "rather than retained at zero", on the grounds that a field naming a
+/// mechanism the pipeline no longer has is actively misleading. None of that
+/// removal had happened. The node was still wired into both shipped pipelines
+/// and still printed its timeout at every startup.
+///
+/// **Presence is not this node's business.** AR-012 moved it to TrackRegistry,
+/// where a window is `[first_seen, last_seen]` of a track an actor owns, and
+/// AR-013 ends that window at the last sighting rather than after it. A
+/// keep-alive here answered the same question a second time and answered it
+/// worse: it re-opened the trailing cool-down the registry exists to refuse.
+///
+/// What a consumer sees change: `--verbosity standard`'s `frames[].identified`
+/// used to list every actor still inside the keep-alive, including ones absent
+/// from the frame. It now lists what was actually matched in that frame. The
+/// minimal and xray outputs are unaffected -- they were already built from
+/// registry claims and never consulted this node.
+
+#include "types.hpp"
+
+#include <string_view>
+#include <utility>
+
+struct FrameAnnotationFunc {
+    static constexpr std::string_view label() { return "frame_annotation"; }
+
+    SceneAnnotation operator()(MatchedSceneFrame mf) {
+        if (mf.source.eof) return {0.0, {}, /*eof=*/true};
+        return {mf.source.timestamp_sec, std::move(mf.actors)};
+    }
+};